The present invention is directed to an anodization process and to the anodized articles formed thereby. In particular, the present invention is concerned with a process for anodizing an article containing a porous oxide-forming metallic layer which is supported by a substrate containing a dielectric.
Articles containing anodized metals, such a anodized porous aluminum oxides on dielectrics, have been prepared and have been suggested for application in metallurgical integrated structures such as magnetic recording heads and in gas or plasma display panels. However, these articles have not been entirely satisfactory and have been difficult to prepare. For instance, it has been difficult to fully anodize all portions of the metal which are to be anodized since a metal member normally anodizes more rapidly at its edges, whereby the internal metallic regions of said member tend to become electrically isolated due to the formation of surrounding, insulating areas of anodized porous metallic material. Once these large internal regions and/or small individual gain regions become electrically isolated from the action of the electrolytic solution due to the action described, it is no longer possible to pass current to the still remaining unanodized metallic regions. Accordingly, the article may contain unwanted, unanodized, interior metal regions, which detract from the usefulness of the article for its intended purpose.
In particular, the presence of nonanodized metallic residue reduces the transparency of an article thereby decreasing its value for use in gas or plasma display panels. Also the presence of nonanodized metallic residue reduces the effectiveness of the anodized porous material as an electrical insulation medium. Due to the presence of the unanodized metal residue, the anodized aluminum retains the ability to act as a partial electrical conductor in a device such as metallurgical structure, which in turn may cause improper circuit connection and/or shorting of the circuit, and/or small current leakage.
Accordingly, the objects of the present invention are to provide an improved method for forming anodized porous layers which at least reduces, If not completely eliminates, the presence of unanodized metal residue in internal regions of the anodized porous layer. It is a further object of the present invention to provide a process for selectively anodizing a porous oxide-forming metallic layer which is relatively inexpensive and easy to carry out successfully.